As generally known in the art, various wireless communication services are provided via wireless communication networks in line with remarkable development of computers, electronics, and communication technologies. The most basic type of a wireless communication service is a voice communication service, which enables wireless voice communication among mobile communication subscribers using their mobile communication terminals regardless of time and place. A wireless data service has recently appeared and enabled mobile communication subscribers on the move to conduct data communication via wireless communication networks with no spatial restrictions.
Therefore, mobile communication subscribers can not only communicate with desired partners at any place and time based on the voice communication service, but also obtain various pieces of daily information (e.g. news, weather, sports, stocks, exchange rates, and traffic) in various forms (e.g. texts, voices, and images) based on the wireless data service even on the move.
Meanwhile, a ringback tone substitution service has recently been developed and welcomed by mobile communication subscribers. This service replaces conventional ringback tones, which are in many cases simple and mechanical sounds (e.g. ringing sounds) generated during call connection and heard by the calling party, with various types of music (e.g. popular songs), recorded voices of the called or calling party, or other types of sounds (e.g. birds singing, aqua sounds, etc) according to the preference of the called or calling party. As such, the ringback tone substitution service gives the calling party listening pleasure with various sound sources instead of boredom from monotonous and mechanical ringback tones.
FIG. 1 is a flowchart showing a conventional method for providing a ringback tone substitute.
When the calling terminal 110 of the calling party originates a call (S102), the caller-side exchange 120 of the mobile communication network informs the called exchange 130 that an originating call has been requested (S104). The called exchange 130 pages the called terminal 140 (S106), and requests the sound source provision device 150 to provide a ringback tone substitute (S108).
The sound source provision device 150 searches for a sound source, which is to be used as a ringback tone substitute for the called party using the called terminal 140 (S110), and transmits the sound source to the calling terminal 110 via the called and caller-side exchanges 130 and 120 (S112). The calling terminal 110 plays the sound source with its voice codec (S114).
When the called exchange 130 receives a response to paging from the called terminal 140 (S116), it informs the caller-side exchange 120 of the incoming call (S118). The caller-side exchange 120 informs the calling terminal 110 that there is a response to the incoming call (S120). Then, the calling and called terminals 110 and 120 conduct voice communication between them (S124).
In the case of such a conventional ringback tone substitution service, the calling terminal 110 decodes a ringback tone substitute sound source, which has been encoded by a voice codec, by using the voice codec and plays it. Recently, most ringback tone substitute sound sources (e.g. popular songs, supporter's songs) have higher sound quality in line with the development of electronic communication technology. However, encoding and decoding of high-quality sound sources by a voice codec degrade the quality of sounds heard by the calling party.
In an attempt to overcome the problem occurring in the conventional ringback tone substitution service based on a voice codec, it has recently been proposed that the mobile communication network provide the calling terminal 110 with a ringback tone substitute sound source by using an audio codec and that the calling terminal 110, which carries both audio and voice codecs, decode the ringback tone substitute sound source by the audio codec and play it.
Although such a ringback tone substitution service based on an audio codec provides higher sound quality than that of the above-mentioned ringback tone substitution service based on a voice codec due to the fact that the mobile communication network provides the calling party 110 with the ringback tone substitute sound source via a voice channel, limitations on the bandwidth of the voice channel, errors during real-time data communication via the voice channel, etc. inevitably degrade the quality to some extent.
Conventionally, synchronous mobile communication networks employ a voice channel having a transmission rate of about 8 kbps, and asynchronous mobile communication networks employ a voice channel having a transmission rate of about 12.2 kbps. However, voice channels having these transmission rates are insufficient for real-time transmission of recent sound source data having CD-grade sound quality. Furthermore, even in the case of a VoIP (Voice over Internet Protocol) system using a data channel to provide a voice communication service, only a small bandwidth is allocated for a voice data service such as the ringback tone substitution service. In the case of a G.729 codec actually used for the VoIP system, a data transmission rate of 8 kbps or 6.4 kbps is supported. Consequently, conventional ringback tone substitution services cannot provide high-quality ringback tone substitutes, because sound sources to be used as ringback tone substitutes are transmitted from the mobile communication network to the calling terminal 110 via a voice channel to which a small bandwidth is allocated.